1. Field of the Invention
The present invention relates to a display, and more particularly, it relates to a display having a pixel portion.
2. Description of the Background Art
A liquid crystal display comprising a pixel portion including a liquid crystal layer is generally known as a display. In the conventional liquid crystal display, the liquid crystal layer of the pixel portion is held between a pixel electrode and a common electrode. The conventional liquid crystal display changes the arrangement of liquid crystal molecules by controlling a voltage (video signal) applied to the pixel electrode of the pixel portion, thereby displaying an image responsive to the video signal on a display portion.
When the aforementioned liquid crystal display applies a dc voltage to the liquid crystals (pixel electrode) of the pixel portion over a long period, an afterimage phenomenon referred to as seizure takes place. Therefore, the liquid crystal display must be driven by a method of inverting the voltage supply source (pixel voltage supply source) of the pixel electrode with respect to that of the common electrode in a prescribed cycle. For example, the liquid crystal display is driven by a DC driving method applying a dc voltage to the common electrode. Line inversion driving inverting the pixel voltage supply source with respect to the common electrode receiving the applied dc voltage every horizontal period is known as such a DC driving method, as disclosed in “Introduction to Liquid Crystal Display Engineering” by Yasoji Suzuki, The Daily Industrial News, Nov. 20, 1998, pp. 101-103. The liquid crystal display completes the operation of writing the video signal in all pixel portions arranged along a gate line every horizontal period.
FIG. 13 is a waveform diagram in a case of driving a liquid crystal display by the conventional line inversion driving method. Referring to FIG. 13, a pixel voltage supply source (video signal) VIDEO is inverted with respect to the voltage supply source COM of a common electrode every horizontal period, in order to drive the liquid crystal display by the conventional line inversion driving method. The pixel voltage supply source (video signal) VIDEO is varied with a displayed image every pixel portions A, B, C, D, E and F.
When the liquid crystal display is driven by the conventional line inversion driving method shown in FIG. 13 at a low frequency in order to reduce power consumption, however, flickering is disadvantageously easy to visually recognize. More specifically, a period for holding the pixel voltage supply source is increased when the liquid crystal display is driven at a low frequency, to remarkably fluctuate the pixel voltage supply source. When the pixel voltage supply source is remarkably fluctuated, the brightness of light passing through the pixel portions A to F deviates from a desired level, to cause flickering. In the conventional line inversion driving method, the aforementioned flickering linearly takes place to easily allow visual recognition.
In this regard, a liquid crystal display employing a dot inversion driving method of inverting a pixel voltage supply source (video signal) VIDEO with respect to the voltage supply source COM of a common electrode every adjacent pixel portions A and B, B and C, C and D, D and E or E and F is proposed in general.
FIG. 14 is a waveform diagram in a case of driving a liquid crystal display by a conventional dot inversion driving method. Referring to FIG. 14, a pixel voltage supply source (video signal) VIDEO responsive to a displayed image is inverted with respect to the voltage supply source COM of a common electrode every pixel portion A, B, C, D, E or F in order to drive the liquid crystal display by the conventional dot inversion driving method, dissimilarly to the conventional line inversion driving method shown in FIG. 13. When the liquid crystal display is driven by this conventional dot inversion driving method, flickering caused by low-frequency driving can be rendered hard to visually recognize since this flickering nonlinearly takes place.
A liquid crystal display capable of negatively/positively reversing images is known in general. This liquid crystal display negatively/positively reverses an image having a white background and black characters to that having a black background and white characters, for example. The liquid crystal display capable of negatively/positively reversing images performs negative/positive reversing by inverting a video signal in a driver IC driving/controlling the liquid crystal display. More specifically, the liquid crystal display inverts the respective bits of a 6-bit video signal, for example, by a video signal inversion circuit including six inverter circuits provided in the driver IC. In general, the liquid crystal display capable of negatively/positively reversing images also displays the images by the aforementioned conventional dot inversion driving method.
However, the conventional dot inversion driving method shown in FIG. 14 requires a video signal having a voltage twice a liquid crystal driving voltage, in order to invert the pixel voltage supply source (video signal) VIDEO with respect to the voltage supply source COM of the common electrode receiving a dc voltage. Assuming that V1 represents the liquid crystal driving voltage in FIG. 14, for example, a video signal having a voltage V2 twice the liquid crystal driving voltage V1 is required in order to obtain the same liquid crystal driving voltage V1 before and after inverting the pixel voltage supply source (video signal) VIDEO with respect to the voltage supply source COM of the common electrode. Therefore, reduction of power consumption is disadvantageously limited also when the liquid crystal display is driven at a low frequency in order to reduce power consumption.
In order to negatively/positively reverse images in the aforementioned liquid crystal display employing the conventional dot inversion driving method, further, the driver IC must disadvantageously be provided therein with a video signal inversion circuit including inverter circuits of the same number as the bit number of the video signal. In order to negatively/positively reverse a 6-bit video signal, for example, the driver IC must include a video signal inversion circuit having six inverter circuits in order to invert the video signal, and hence the structure of the video signal inversion circuit is complicated and the driver IC remarkably consumes power when reversing the images.